What are void (self-closing) elements in HTML?

0-2 years experience

1. 1You need to add an image to a page. How would you write the HTML tag, and why don't you need a closing tag?
2. 2If you accidentally write <br></br> in your markup, what will the browser do, and is it valid?
3. 3When you create a custom component that renders an <input> element, what must you remember about its markup?

2-5 years experience

1. 1Your team notices that a form's submit button sometimes doesn't appear in older browsers. You discover the <input type='submit'> tag was written with a closing tag. Explain why this could cause issues and how you'd fix it.
2. 2During a refactor, a colleague changed <img src='...'> to <img src='...'></img>. The page layout broke. Walk me through why that happened and how you'd debug it.
3. 3You are building a markdown‑to‑HTML converter. How would you ensure that void elements are emitted correctly, and what edge cases would you watch for?

5-8 years experience

1. 1Our design system includes a component library that renders many void elements (img, input, br). At scale, we need to enforce correct markup across multiple teams. How would you design a linting or build‑time check to catch misuse of void elements?
2. 2We are migrating a legacy HTML codebase to a component framework that requires JSX syntax, where void elements must be self‑closing. What challenges arise, and how would you handle cases where existing markup uses closing tags?
3. 3Explain any performance implications of incorrectly closing void elements in a large single‑page application, especially regarding DOM diffing and re‑rendering.

8+ years experience

1. 1Our organization is standardizing on a universal component library used across web, mobile web, and email templates. How would you architect the handling of void elements to ensure consistency, accessibility, and compatibility across these platforms, given differences in rendering engines?
2. 2When planning a long‑term migration from HTML5 to a custom XML‑based UI language, how would you map HTML void elements, and what strategies would you use to avoid breaking existing content and SEO?
3. 3Discuss the trade‑offs of enforcing strict HTML validation for void elements in a CI pipeline versus allowing flexibility for third‑party content.